Nanostructured chemicals are best exemplified by those based on low-cost Polyhedral Oligomeric Silsesquioxanes (POSS) and Polyhedral Oligomeric Silicates (POS). POSS and POS systems contain hybrid (i.e. organic-inorganic) compositions in which the internal cage framework is primarily comprised of rigid inorganic silicon-oxygen bonds. The exterior of the nanostructure is covered by both reactive and nonreactive organic functionalities (R), which ensure compatibility and tailorability of the nanostructure with organic and inorganic materials. These and other properties and features of nanostructured chemicals are discussed in detail in U.S. Pat. Nos. 5,412,053 and 5,484,867, which are incorporated herein by reference.
Current engineering methods produce POSS silanols bearing one through four silanol groups per cage. Control over the stereochemistry and silation of the silanols has been discussed extensively in the U.S. Pat. No. 6,660,823, and a significant number of POSS silanols and POSS siloxide anions have become items of commerce.
Certain microelectronic, medical, catalytic, and biological applications could benefit from POSS silanols containing mixtures of R groups on the cage where one or more types of R group are greatly different in reactivity or properties (e.g. hydrophilic vs hydrophobic) from other R groups on the cage. Under such a scenario it would be desirable to maintain the silanol groups for bonding to metallic, biological, or polymeric surfaces, via covalent silation, hydrogen bonding, ion paring, or Van der Waals contact. Thus a need exists to provide POSS silanols bearing one or more different R groups on the same POSS silanol cage molecule. It is especially desirable to produce POSS cages with reactive olefinic groups R2 which can participate in other chemistry than that available to the R1 groups and the silanols or siloxides (FIG. 1).
A key to the utility of POSS molecules and their compatibility with man-made and organic materials and surfaces is that their dispersion is thermodynamically governed by the Gibbs free energy of mixing equation (ΔG=ΔH−TΔS). The nature of the R group and ability of the reactive groups on the POSS cage to react or interact with polymers and surfaces greatly contributes to a favorable enthalpic (ΔH) term while the entropic term (ΔS) is highly favorable when the cage size is monoscopic.
Consequently a need exists for improvement upon the prior art of POSS cage compositions. An improved process yielding high purity and molecularly precise POSS silanols or POSS siloxides bearing combinations of hydrophobic and hydrophilic and saturated and unsaturated R groups on the same molecule is described.